Roger Federer and Rafael Nadal will meet Thursday evening in a quarterfinal at the BNP Paribas Open in Indian Wells, Calif., their 29th career match. In several ways, it will be unlike any of their previous 28 meetings.

If a quarterfinal seems unworthy of their nine-year-old rivalry, one of the best in tennis history, it may be because they have never played in a quarterfinal before. Also, one player or the other has been ailing heading in to some of their previous meetings, but never before have both been so conspicuously struggling with injuries or recovery from injury. And this will be their first meeting since the ATP World Tour started more aggressively enforcing the time-violation rule, which has both angered Nadal and has sped up his game. So the match could be over a bit sooner than expected.

Nadal and Federer first met in Miami in 2004, when Nadal was just 17 years old and Federer was the top-ranked player in the world. In a way, it was a preview of things to come: Nadal straight-setted Federer (Nadal owns the career head-to-head, 18-10, though since that Miami match Federer has won six of their 10 meetings on hard courts, which are the surface used at Indian Wells). In a way, though, it wasn’t a typical match at all, because it came in the round of 32. Since then, they’ve met 27 times — once in the round robin of the 2011 World Tour Finals, and 26 times in semifinals or finals. That streak is the third longest in tennis history, not counting round robins: Jimmy Connors had 28 straight semifinal or final meetings with Ivan Lendl, and Connors also had 27 straight meetings in the final four or later against John McEnroe.

In an ominous sign for fans of the Federer-Nadal rivalry, after those Connors streaks ended, he barely played those rivals at all afterward. Connors beat McEnroe in a 1987 quarterfinal, and played just two more times, each straight-set routs, even though McEnroe remained active on tour for five more years. And after Connors’s last semifinal against Lendl, in 1988, he faced Lendl just once more, in a U.S. Open second-round meeting that ended with a Lendl bagel set. That is, they met just once in Lendl’s last six years on tour.

It’s simply easier and more likely for two players to meet when they are ranked first and second and consistently beat everyone else on tour. Nadal and Federer haven’t combined to own the top two spots since Indian Wells two years ago, meaning they likely won’t meet unless they’re drawn into each other’s halves or quarters of draw, or if one or both benefit from upsets or beat players ranked higher than them. Even before their first quarterfinal tonight, their rivalry already had moved into a less frequent, less intense phase. Over a period of four years and three months through the 2009 Madrid final, they met 17 times, including 15 finals and two semifinals. In the nearly four years since, they’ve met eight times — Thursday’s will be the ninth — and just three were finals.

That each man even reached the quarterfinal is impressive, given that each has had to fight against upstart opponents and their own bodies to get there. Federer, at age 31, has struggled with his back in his last two matches, while Nadal, age 26, says he still isn’t fully recovered from a knee injury that kept him off tour for seven months, until last month; and off hard courts for nearly a year. Both men needed to win a third set, 7-5, late on Wednesday to advance to the quarterfinals. Federer said afterward that with their injuries he and Nadal “are both a bit suspect.” And Nadal sounded even less confident, saying, “This match arrives too early for me to go to the match with the feeling that I can play equal conditions. Two weeks ago, I didn’t know if I would be able to be here. Being in quarterfinals is a fantastic result for me, and we’ll see.”

None of this inspires confidence that their 29th meeting will be a classic, and in truth many of their recent matches haven’t reached the heights of some of their earlier meetings. Of their last nine matches — of which Nadal has won five — five were straight-setters and neither of the two best-of-five matches went to a fifth set, after five of their earlier meetings went five sets. Even if it is a classic, it could be a comparatively fast one. The ATP has begun to enforce its rule limiting time between points to 25 seconds with more consistency, a decision Nadal has criticized for potentially limiting classic, long rallies. Earlier in the season, before Nadal’s return, there were signs that the rule had, in fact, sped up the game. At Indian Wells, it seems to have sped up Nadal’s game. (Federer, one of the fastest between points on tour, has supported enforcing the time rule.)

Nadal’s two matches this year at Indian Wells have moved along at 45.3 seconds per point, brisk compared to his pace of 50.1 seconds per point at Indian Wells last year in his four matches before his semifinal meeting with Federer. These figures aren’t the same as time between points — they count all time during matches, including rallies and time during changeovers. (The ATP doesn’t track and publish time between points with regularity.) And they don’t adjust for the pace of Nadal’s opponents. But they do suggest that not only has the rule gotten his anger, it’s also gotten his attention.

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